NSW chief health officer Kerry Chant said authorities would do genomic sequencing in an attempt to track it down.

But she said the "jigsaw puzzle sometimes has empty black spaces" despite the best detective work.

The cluster stands at eight people, only one of whom is a local resident.

Four cases from one family were diagnosed earlier and another four in the 24 hours to Sunday night.

One is a staff member, two had a meal there and one was a contact, NSW health authorities said on Monday. The club has been closed for two weeks.

On Monday, as Batemans Bay residents joined long queues for testing, Eurobodalla Shire Mayor Liz Innes has asked people to stay home if they could and to limit travel.

"I know the constantly changing advice is exhausting for businesses, but if you don't have a COVID-safe plan in place already, please get on to it today," she said. "Lives could depend on this."

NSW Health is now directing people who visited the Batemans Bay Soldiers Club on Monday 13 July, Wednesday 15 July, Thursday 16 July and Friday 17 July, to immediately be tested for COVID-19 and self-isolate for 14 days, regardless of symptoms.

Those people must stay in isolation for a full 14 days even if their test is negative. Anyone who develops COVID-19 symptoms should also be retested, even if they have had a negative result previously.

People who were at the club on Tuesday, July 14, are advised to monitor for symptoms and seek testing if symptoms develop.

Pop-up testing clinics attracted long queues.

READ MORE:

NSW reported 20 new cases in the 24 hours to 8pm on Sunday, all linked to known clusters - the Crossroads Hotel (now 48 cases), the Thai Rock restaurant and the Batemans Bay Soldiers Club.

NSW Premier Gladys Berejiklian said the next few weeks were critical. She urged people to avoid large crowds and think twice about going into any crowded place even with social distancing.

"I cant say enough how stressed and worried I am about the next few weeks," she said.

"We are at a critical point in our state's ability to deal with the pandemic ...

"All of us have to really think about what we're doing in the next few weeks. The next few weeks are absolutely critical."

If NSW got through the next three for four weeks and stayed on top of the seeding from Victoria and current outbreaks, the state could have "medium to long term surety" that it could keep moving forward, she said.

NSW has two people intensive care, one aged in their 30s.

NSW Police Minister David Elliott said he was especially concerned about Batemans Bay because of the ageing population and the number of visitors over the school holidays.

Batemans Bay Soldiers Club chief executive Paul Biddlestone said many of the 100 or so staff who worked last week had been tested, but others were queuing for a test on Monday.

"There are a few of us who have been stuck in queues and turned around," Mr Biddlestone said.